Light is a complex phenomenon that may be explained with a simple model based on rays and wave-fronts.
Visible light represents only a small portion of the entire electromagnetic spectrum of radiation that extends from high-frequency gamma rays through X-rays, ultraviolet light, infrared radiation and microwaves to very low frequency long-wavelength radio waves.
Very high-frequency electromagnetic radiation such a gamma rays, X-rays, and ultraviolet light possess very short wavelengths and a great deal of energy. On the other hand, lower frequency radiation such as visible, infrared, microwave, and radio waves have correspondingly greater wavelengths with lower frequencies and energy. The vast majority of the light we see is emitted from the sun, which also emits many other frequencies of radiation that do not fall in the visible range. When indoors, we are exposed to visible light that comes from “artificial” sources primarily originating from fluorescent and/or tungsten devices.
Reflection of light and other forms of electromagnetic radiation occur when waves encounter a boundary that does not absorb the radiation's energy and bounces the waves off the surface. The incoming light wave is referred to as an incident wave and the wave that is bounced from the surface is called the reflected wave.
The refraction of visible light is an important characteristic of lenses that allows them to focus a beam of light onto a single point. Refraction, or bending of the light, occurs as light passes from a one medium to another when there is a difference in the index of refraction between the two materials.
Diffraction of light occurs when a light wave passes by a corner or through an opening or slit that is physically the approximate size of, or even smaller than, that light wave's wavelength. Diffraction describes a specialized case of light scattering in which an object with regularly repeating features, such as a diffraction grating, produces an orderly diffraction of light in a diffraction pattern. In the real world most objects are very complex in shape and should be considered to be composed of many individual diffraction features that can collectively produce a random scattering of light.
Natural sunlight and most forms of artificial illumination transmit light waves whose electric field vectors vibrate in all perpendicular planes with respect to the direction of propagation. When the electric field vectors are restricted to a single plane by filtration then the light is said to be polarized with respect to the direction of propagation and all waves vibrate in the same plane.
An important characteristic of light waves is their ability, under certain circumstances, to interfere with one another. One of the best examples of interference is demonstrated by the light reflected from a film of oil floating on water or a soap bubble, which reflects a variety of beautiful colors when illuminated by natural or artificial light sources.
Anisotropic crystals have crystallographically distinct axes and interact with light in a manner that is dependent upon the orientation of the crystalline lattice with respect to the incident light. When light enters a non-equivalent axis in an anisotropic crystal, it is refracted into two rays each polarized with the vibration directions oriented at right angles to one another, and traveling at different velocities. This phenomenon is termed “double-” or “bi-refraction” or “bi-refringence” and is seen to a greater or lesser degree in all anisotropic crystals.
This phenomenon can be duplicated using other means such as photoelasticity and stress Refringence. Photoelasticity is the property of some materials (including most plastics) that compression can cause birefringence. The effect is also known as mechanical birefringence or stress refringence. Stress Refringence is the phenomenon that occurs when certain transparent or translucent materials are subjected to external or internal stresses. The existing stress, which usually varies from point to point, causes local changes in the index of refraction. This in turn means variations in the speed of light through the material. When coming from a beam of polarized light, individual rays take different paths through the material and, upon recombining, produce interference patterns. Properly interpreted, lines of the same refringence indicate points in the material of the same stress. This is the principle that underlies the technique of photoelasticity.
Further, bi-refringence may be created using Oriented polymer films. The oriented polymer film has polymer chains oriented along an axis, effectively creating a crystal structure as described in the definitions above. By applying numerous layers of varied thickness and orientation, you can further modify the local index of refraction and corresponding patterns of birefringence.
Another means of creating the phenomenon is Stressed Transparent objects. Stressed Transparent objects are created by varying the stress in a transparent object (be it of acrylic, glass, or any transparent object) color may be created (as described above) through the variation of the stress patterns. The patterns are created from the photoelastic effect or stress refringence.
The concept of color temperature is based on the relationship between the temperature and radiation emitted by a theoretical standardized material termed a black body radiator cooled down to a state in which all molecular motion has ceased. This model is useful in relating the emission spectrum of natural and artificial light sources to the emulsion characteristics of individual photographic films and electronic digital cameras.
Visible light contains primary colors that are fundamental to human color vision. The primary additive colors are red, green, and blue, while the primary subtractive colors are cyan, magenta, and yellow. Adding the primary additive colors together in equal portions yields white, and adding the primary subtractive colors together (also in equal portions) yields black.
Most natural and artificial light sources emit a broad range of wavelengths that cover the entire visible light spectrum. However, it is often desirable to produce light that has a restricted wavelength spectrum. This can be easily accomplished through the use of specialized filters that transmit some wavelengths and selectively absorb or reflect unwanted wavelengths.
Glass lenses are composed of glass or transparent plastic, which allow light to be focused, magnified, and/or scattered to produce a wide spectrum of effects. Most lenses have two surfaces that are ground and polished in a specific manner designed to produce either a convergence or divergence of light passing through the lens.